I. Field of the Invention
The invention relates to a method and apparatus for applying a protective shield to the tool joint and collars of a drill pipe.
II. Description of the Prior Art
Drill pipes utilized in drilling oil and gas wells are rapidly rotated in a bore hole in the earth's surface. In drilling a bore hole, the drill string rotates and simultaneously applies downward force to the drill bit forming the hole. The weight of the drill string, which may be thousands of feet in length, tends to cause the drill pipe to buckle or bend in the long length between the surface of the earth where the drilling rig is located and the bit penetrating deep within the earth. This bending causes the drill pipe to tend to rub on the bore hole. In addition, most bore holes depart from true vertical. In some instances, holes are drilled intentionally directionally so that from a given spot on the earth the bottom of the bore hole may be displaced laterally a considerable distance. Even when bore holes are not intentionally drilled directionally, it is exceedingly difficult to keep a bore hole in absolute vertical orientation. This departure from the vertical further causes the drill pipe to rub against the side wall of the bore hole. After a bore hole is advanced into the earth it is common procedure to line it with casing in which event at least the upper portion of the drill string is rotating within the casing. The casing provides an even smaller area for receiving the rotating drill pipe and increases the propensity of the drill pipe to rub as it is rotated inside the casing causing wear on both the drill string and the casing.
A typical length of drill pipe has a male threaded joint at one end and a female threaded joint at the other. To increase the strength of the area where the joints are made, the drill pipe is usually of increased diameter at the ends. These enlarged diameter portions of drill pipe are called "tool joints". Since they are larger in diameter than the pipe itself the tool joints usually receive the greatest amount of wear. However, in some conditions the middle of a length of drill pipe can also engage the bore hole or casing and be worn through long usages.
Others, combating the problem of the wear of drill pipe, and the particular wear at the tool joints, have provided hard surfacing of the surfaces of the tool joints. This is usually applied by electric welding of a hard material onto the outside surface of the tool joints. Tungston carbide is frequently used in such applications. Others have provided removable or detachable drill pipe protectors. These may be metal or non-metal although the use of non-metal protectors are the most common. The removable drill pipe protectors are usually bifurcated devices which are hinged at one side and are placed around the tool joint. A pin is used on the side opposite the hinge.
One difficulty with such removable type of drill pipe protectors is that of keeping them in position in the proper place on the tool joints. U.S. Pat. No. 3,942,824 shows a type of tool joint protector of a non-metallic type which includes a flange intended to keep the protector in position on an assembled tool joint. One problem with this type of device is that the finished diameter of the protector may be excessively large for the internal diameter of the casing in which the drill string is utilized thus causing drilling fluid flow restrictions.
Another type of tool joint protector is illustrated in U.S. Pat. No. 1,814,183 in which a dove-tail shaped groove is formed in a coupling which receives a mating rubber material. This type of protector requires specific machining of the tool joint and the rubber portion is difficult to replace when it becomes worn.
Most of the known type tool joint protectors require the drill string to be taken to a manufacturing plant where the protectors are applied. For instance, when a welded-on hard surface material is applied to a tool joint some means must be provided for supporting the pipe and rotating it during the application of the hard surface material.
An object of the present invention is to provide a method of installing a tool joint protector which overcomes limitations and difficulties with known types of protectors available on the market today.
A specific object of the invention is to provide a method of applying a protector to a drill string tool joint which can be easily accomplished in the field without requiring that the tool joint be rotated during the application of the protector.